Many industrial operations such as refineries, steel mills, chemical factories, electrical distribution, and other operations result in the formation of by-products consisting of oily liquids, or organic contaminated sludges, sediments, soils, and solids. The aforementioned oily liquids, oily sludges, and organic contaminated sludges, soils, and solids, comprise various mixtures of oils (including a multitude of oily organic compounds) and water. These oily and organic matter containing wastes have been found to be environmentally damaging and in many cases--notably when the contaminant includes pesticides or polychlorinated biphenyls (PCBs)--is dangerous to human health. The aforementioned oily and organic material containing wastes have proven difficult and expensive to separate into components. They have also proven difficult to remove the undesirable components or to render them environmentally acceptable. In consequence, in the past, the oily and organic material containing wastes were often simply impounded in ever enlarging ponds, lagoons, or dumps. Many such contaminated sites now exist, are deemed hazardous and undesirable, and Environmental Protection Agency regulations require their clean-up. Clearly, there exists a requirement for an oil and organic material waste treatment procedure which is both effective and economical.
A large number of techniques have been proposed, tried, and even patented to deal with the above described problem. These techniques may be divided into various types. One of the most favored technique types is incineration. Another highly favored technique type is solvent extraction. Both of these technique types have been classified by the Environmental Protection Agency as Best Available Technology (BAT).
The present invention consists of an improvement to solvent extraction methods. The improvement is particularly advantageous when practicing a hot solvent extraction, wherein the oily or organic material contaminated soil, sludge, or liquid is extracted with a solvent at temperatures above about 100.degree. F., with the solvent at that temperature possessing a limited solvent capability for water. Hot solvent extraction is frequently used for final cleaning of organic material contaminated solids which have been dewatered and partially organic material extracted by the B.E.S.T.(R) solvent extraction process. The B.E.S.T. process is described in U.S. Pat. No. 3,899,419, issued to Emmanual, the disclosure of which is incorporated herein by reference. Improvements on the Emanual process are disclosed in U.S. Pat. No. 3,925,201 to Ames, U.S. Pat. No. 4,056,466 to Peters, U.S. Pat. No. 4,830,754 to Nowak et al, and U.S. Pat. No. 5,047,153 to Nowak et al, each of which is incorporated, in its entirety, by reference.
The B.E.S.T. process consists of:
1) mixing the oily waste to be treated with an adequate amount of solvent having an inverse critical solution temperature such as triethylamine at a temperature below the inverse critical solution temperature (15.5.degree. for triethylamine). The oily material, water, and solvent will form one homogeneous liquid phase. PA1 2) Separating the solid phase (if one exists) from the liquid phase which contains the oily material, water, and solvent. PA1 3) Heating the liquid phase above the inverse critical solution temperature of the solvent. Two phases will form--a water phase in which a small amount of solvent is soluble--and a solvent phase in which the oily material is soluble along with a small amount of dissolved water (about 2% at 60.degree. C. for triethylamine). PA1 4) Separating the water phase by stripping and recovering the solvent. The water can be discharged. PA1 5) Purifying the water phase by stripping and recovering the solvent. The water can be discharged. PA1 6) Separating the oily material from the solvent phase, usually by distilling the solvent away. The oily material can be reused, incinerated, or otherwise treated. The solvent is reused. The solvent, unless specially treated, will contain the water which was dissolved in the solvent phase. PA1 7) The solid can be dried to recover solvent and discharged if sufficiently cleaned of the oily or organic material contaminant. If more oily contaminant must be removed, the solid is treated again with solvent using a Hot Solvent Extraction process. However, in this solvent treatment step hot solvent (above the inverse critical solution temperature) is used since essentially all the original water has been separated from the solid and since solubility of the oily material in the solvent is enhanced at high temperature.
The B.E.S.T. process described above works well to achieve its purpose of dewatering and removing oily or organic material contaminant material from oily wastes. However, problems sometimes occur in the subsequent solid cleanup using the hot solvent extraction process (Step 7 above), especially with clay or clay-like or clay containing solids. Solids separated from the cold extraction (below the inverse critical solution temperature) are mixed with hot solvent (above about 100.degree. F.) in the hot solvent extraction process (Step 7 above), especially with clay or clay-like or clay containing solids. When the solids separated from the cold extraction (below the inverse critical solution temperature) are mixed with hot solvent (above about 100.degree. F.) in the hot solvent extraction Process, agglomeration of the solids occurs and either a sticky, doughy mass or a multitude of hard spheres about the size of small peas to marbles is formed. Mixing and handling of the solids becomes difficult, power requirements are increased as is equipment strength requirements, and extraction efficiency is reduced. Solids of similar characteristics (clay, clay-like or clay containing solids which are oil or organic material contaminated and containing water in amounts from about 1% to about 50%) produced by treatment processes other than B.E.S.T. or naturally occurring react in the manner described above when treated by the hot solvent extraction process and present the problems described above.
Clearly, a method is needed to prevent agglomeration of solids and to prevent loss of extraction of oily or organic containing material from solids during the aforesaid hot extraction steps of the B.E.S.T. process.